This section is intended to provide a background or context to the invention that is recited in the claims. The description herein may include concepts that could be pursued, but are not necessarily ones that have been previously conceived or pursued. Therefore, unless otherwise indicated herein, what is described in this section is not prior art to the description and claims in this application and is not admitted to be prior art by inclusion in this section.
The following abbreviations that may be found in the specification and/or the drawing figures are defined as follows:                3GPP third generation partnership project        BW bandwidth        CA carrier aggregation        CC component carrier        CDM code division multiplexing        DL downlink (eNB towards UE)        eNB E-UTRAN Node B (evolved Node B)        EPC evolved packet core        E-UTRAN evolved UTRAN (LTE)        HARQ hybrid automatic repeat request        LTE long term evolution of UTRAN (E-UTRAN)        MAC medium access control (layer 2, L2)        MM/MME mobility management/mobility management entity        Node B base station        O&M operations and maintenance        OFDMA orthogonal frequency division multiple access        PCC primary component carrier        PDCP packet data convergence protocol        PHY physical (layer 1, L1)        RLC radio link control        RRC radio resource control        RRM radio resource management        SC-FDMA single carrier, frequency division multiple access        SCC secondary component carrier        SFN system frame number        S-GW serving gateway        SI system information        TTI transmission time interval        UE user equipment, such as a mobile station or mobile terminal        UL uplink (UE towards eNB)        UTRAN universal terrestrial radio access network        
A communication system known as evolved UTRAN (E-UTRAN, also referred to as UTRAN-LTE or as E-UTRA) has been specified within 3GPP. The DL access technique is OFDMA, and the UL access technique is SC-FDMA.
One specification of interest is 3GPP TS 36.300, V9.2.0 (2010-01), “3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Evolved Universal Terrestrial Radio Access (E-UTRA) and Evolved Universal Terrestrial Access Network (E-UTRAN); Overall description; Stage 2 (Release 9)”, incorporated by reference herein in its entirety.
FIG. 1 reproduces FIG. 4-1 of 3GPP TS 36.300, and shows the overall architecture of the E-UTRAN system. The E-UTRAN system includes eNBs, providing the E-UTRA user plane (PDCP/RLC/MAC/PHY) and control plane (RRC) protocol terminations towards the UE (not shown). The eNBs are interconnected with each other by means of an X2 interface. The eNBs are also connected by means of an S1 interface to an EPC, more specifically to a MME (Mobility Management Entity) by means of a S1 MME interface and to a Serving Gateway (SGW) by means of a S1 interface. The S1 interface supports a many-to-many relationship between MMEs/S-GW and eNBs.
The eNB hosts the following functions:                functions for RRM: Radio Bearer Control, Radio Admission Control, Connection Mobility Control, Dynamic allocation of resources to UEs in both UL and DL (scheduling);        IP header compression and encryption of the user data stream;        selection of a MME at UE attachment;        routing of User Plane data towards the Serving Gateway;        scheduling and transmission of paging messages (originated from the MME);        scheduling and transmission of broadcast information (originated from the MME or O&M); and        a measurement and measurement reporting configuration for mobility and scheduling.        
Of particular interest herein are the further releases of 3GPP LTE targeted towards future IMT-Advanced systems, referred to herein for convenience simply as LTE-Advanced (LTE-A). LTE-A is directed toward extending and optimizing the 3GPP LTE Release 8 radio access technologies to provide higher data rates at very low cost. LTE-A will most likely be part of LTE Release 10. LTE-A is expected to use a mix of local area and wide area optimization techniques to fulfill the ITU-R requirements for IMT-Advanced while keeping the backward compatibility with LTE Release 8. Topics that are included within the ongoing study item include bandwidth extensions beyond 20 MHz, among others.
The bandwidth extension beyond 20 MHz in LTE-Advanced may be done via carrier aggregation (CA), in which several Release 8 compatible carriers are aggregated together to form a system bandwidth (aggregations of larger or smaller component carriers is also possible). This is shown by example at FIG. 2 in which there are 5 Release 8 compatible CCs aggregated to form one larger LTE-Advanced bandwidth. A purpose for aggregating individual e.g. 20 MHz Release 8 compatible component carriers (CCs) is that each existing Release 8 terminal can receive and/or transmit on one of the CCs, whereas future LTE-Advanced terminals could potentially receive/transmit on multiple CCs at the same time, thus having support for a large bandwidth. FIG. 2 is specific to LTE-Advanced but makes clear the general concept of CA regardless of what size the CCs; for example smaller frequency chunks such as 10 MHz CCs may be aggregated to get a 20 MHz bandwidth and CCs may be made larger than 20 MHz. LTE Release 8 allows bandwidths of 1.4 MHz, 5 MHz and 10 MHz as well as 20 MHz, so any of these may be the size of a CC. See further 3GPP TS 36.912.
A principle of carrier aggregation is illustrated in FIG. 2. In 3GPP Release 8 UEs are assumed to be served by a stand-alone CC, while in LTE-Advanced terminals can receive or transmit simultaneously on multiple aggregated CCs in the same TTI.
A Release 10 UE may not necessarily be scheduled across the entire five CCs shown by example at FIG. 2 (or however many total CCs there are in the whole bandwidth), but rather there may be a subset of CCs for which the UE is configured to use, e.g., via RRC signaling. This avoids the UE having to blind detect on every possible CC in the whole bandwidth to find the appropriate SI, a power intensive operation.
In Release 8, there is only one carrier and the UE keeps up-to-date system information by performing system information (SI) acquisition and SI update upon receiving SI modification notification on that carrier, or by reading a specific parameter (e.g., a ‘value tag’) in one of the broadcast SI messages (e.g., a SIB1 message). A modification period is used to ensure all the UE within the cell apply changes to system information at specific radio frames (e.g., at modification boundary), see further 3GPP TS 36.331.
For carrier aggregation, a UE maintains valid system information for more than one CC. The SI acquisition on the ‘main CC’ (e.g., on the PCC) may be implemented as in Release 8. However, applying the Release 8 mechanisms to all CCs (e.g., to the SCCs) may not be feasible. It was agreed in R2-100826, Report of 3GPP TSG RAN WG2 meeting #68 that “Having the UE monitor SI change paging notification on all configured CCs, or have the UE periodically read the SIB1 on all configured CCs, is not an acceptable solution”.
For carrier aggregation, a UE maintains valid system information for the PCC and for one or more SCCs. In regards to UE power consumption and complexity, applying the Release 8 mechanisms to all CCs is not practical. The modification period of each CC may differ. Further, the timing of the SI change may be even more problematic as the SFNs may not be aligned across all CCs. The potential to aggregate CCs from non-co-located eNBs may be useful in future releases. In case of non-co-located eNBs, the alignment of SFNs over the CCs may be exceptionally difficult. Therefore, in order to have a future-proof mechanism, it may not be useful to assume that the SFNs (and/or modification periods) are the same across the CCs.
It has been considered to have SI change notification of other CCs in paging message of the anchor cell or serving cell (or the PCC), UEs may read the system information of the other CCs upon receiving such notification. The considered paging message is modified over the paging messages of the previous releases which may imply that the new paging message may not be received by legacy UEs, thus reducing paging capacity. Additionally, such a method ignores that the modification periods may be different in PCC and SCCs. The UE may still need to perform SI acquisition on multiple CC (which results in unnecessary activation of CCs). See further, R2-100413, “System Information Acquisition for Carrier Aggregation” and R2-101075, “Primary Component Carrier”.
Another potential approach is to use dedicated RRC signaling with modified SI from either a special cell or any activated CCs. Such a method cannot ensure that all the UEs receive and correctly decode the dedicated signaling for SI updates at the same time, which may lead to UEs within a cell having differing versions of the current system information at a given time. See further, R2-100536, “Remaining Issues in System Information Delivery”.
In cellular systems, a specific ‘starting time’ parameter may be used to indicate the moment, when the new parameters are taken into use. The addition and removal of new carriers in the frequency hopping sequence may be performed with a command including the ‘starting time’ parameter in order to ensure that all UEs change the hopping sequence at the same time (see further 3GPP TS 44.018, section 10.5.2.38). However, the starting time is limited to a single event, while in a case where multiple events may need to be signaled, for example, where multiple SI of multiple CCs may be updated, but they are taken into use at different times (e.g., at a modification boundary of the given CC). Additionally, modification boundary information may refer to repetitive instances of time, while a starting time refers to a single point of time.
What is needed is a solution for SI updates for multiple CCs so that the new information may be used by all UEs at the correct time even when the multiple CCs are not aligned.